Method for producing nickel powder

ABSTRACT

Provided is a method for producing fine nickel powder used as suitable seed crystals for producing nickel powder from a solution containing a nickel ammine sulfate complex. The method for producing nickel powder sequentially comprises: a mixing step of adding, to a solution containing a nickel ammine sulfate complex, an insoluble solid which is insoluble in the solution to form a mixed slurry; a reduction and precipitation step of charging a reaction vessel with the mixed slurry and then blowing hydrogen gas into the mixed slurry in the reaction vessel to reduce nickel complex ions contained in the mixed slurry to form nickel precipitate on a surface of the insoluble solid; and a separation step of separating the nickel precipitate on the surface of the insoluble solid from the surface of the insoluble solid to form nickel powder.

BACKGROUND

1. Field of the Invention.

The present invention relates to a method for producing fine nickelpowder that can be utilized as seed crystals from a solution containinga nickel ammine sulfate complex, and particularly, the present inventioncan be applied to the treatment of an in-process intermediate solutiongenerated from a nickel hydrometallurgical process.

2. Description of the Related Art.

Examples of known methods for producing fine nickel powder include drymethods such as an atomizing method of dispersing molten nickel in a gasor in water to obtain fine powder and a CVD method of volatilizingnickel and reducing it in a vapor phase to thereby obtain nickel powderas shown in Japanese Patent Laid-Open No. 2005-505695.

Further, examples of methods for producing nickel powder by a wetprocess include a method of producing nickel powder using a reducingagent as shown in Japanese Patent Laid-Open No. 2010-242143 and a spraypyrolysis method in which nickel powder is obtained by pyrolysisreaction by spraying a nickel solution into a reducing atmosphere athigh temperatures as shown in Japanese Patent No. 4286220.

However, these methods are not economical because they require expensivereagents and a large amount of energy.

On the other hand, a method of obtaining nickel powder by feedinghydrogen gas into a nickel ammine sulfate complex solution to reducenickel ions in the complex solution as shown in “The Manufacture andproperties of Metal powder produced by the gaseous reduction of aqueoussolutions”, Powder metallurgy, No. 1/2 (1958), pp 40-52. is industriallyinexpensive and useful. However, nickel powder particles obtained bythis method are easily coarsened, and it has been difficult to producefine powder that can be used as seed crystals.

Particularly, when particles are intended to be generated from anaqueous solution and grown, there is used a method of obtaining a powderhaving a predetermined particle size by allowing a small amount of finecrystals called seed crystals to coexist and feeding a reducing agentthereto to grow the seed crystals. Although seed crystals used in thismethod are obtained by grinding products in many cases, time and effortare required and the yield decreases, which leads to an increase incost. Further, seed crystals having the best particle size andproperties are not necessarily obtained by grinding. Thus, a method forstably obtaining seed crystals has been required.

In such a situation, the present invention provides a method forproducing fine nickel powder used as suitable seed crystals forproducing nickel powder from a solution containing a nickel amminesulfate complex.

SUMMARY

A first aspect of the invention to solve such a problem is a method forproducing nickel powder, sequentially comprising: a mixing step ofadding, to a solution containing a nickel ammine sulfate complex, aninsoluble solid which is insoluble in the solution to form a mixedslurry; a reduction and precipitation step of charging a reaction vesselwith the mixed slurry and then blowing hydrogen gas into the mixedslurry while maintaining a pressure of a gas phase part in the reactionvessel at 1.0 to 4.0 MPa, to reduce nickel complex ions contained in themixed slurry to form nickel precipitate on a surface of the insolublesolid; and a separation step of separating the nickel precipitate on thesurface of the insoluble solid from the surface of the insoluble solidto form nickel powder.

A second aspect of the invention is a method for producing nickel powderaccording to the first aspect, wherein the concentration of ammoniumsulfate in the solution containing a nickel ammine sulfate complex is inthe range of 10 to 500 g/L.

A third aspect of the invention is a method for producing nickel powderaccording to the first and second aspects, wherein, in the reductionstep, the temperature of the mixed slurry when hydrogen gas is blown is150 to 200° C.

A fifth aspect of the invention is a method for producing nickel powderaccording to the first to third aspects, wherein the insoluble solid isone or a combination selected from among nickel, alumina, zirconia,iron, and silica.

The present invention can provide a method for producing the best finenickel powder as seed crystals used for producing nickel powder moreeconomically and efficiently from a nickel ammine sulfate complexsolution using hydrogen gas.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a production flow chart of the method for producing nickelpowder according to the present invention.

FIG. 2 is a SEM image showing the appearance of nickel powder producedin Reference Example 1.

FIG. 3 is a SEM image showing the appearance of nickel powder producedin Reference Example 2.

FIG. 4 is a SEM image showing the appearance of nickel powder producedin Example 1.

FIG. 5 is a SEM image showing the appearance of nickel powder producedin Reference Example 4.

FIG. 6 is a SEM image showing the appearance of nickel powder producedin Reference Example 5.

DETAILED DESCRIPTION

The present invention provides a method for producing nickel powder,characterized by adding, to a nickel ammine sulfate complex solution, aninsoluble solid which is insoluble in the solution or the insolublesolid and a dispersant to form a mixed slurry and then blowing hydrogengas into the mixed slurry to thereby produce nickel powder.

Hereinafter, the method for producing nickel powder according to theinvention will be described with reference to the production flow chartshown in FIG. 1.

[Nickel Aramine Sulfate Complex Solution]

Examples of a suitable nickel ammine sulfate complex solution used inthe present invention include, but are not limited to, one obtained bydissolving a nickel-containing material such as an industrialintermediate comprising one or a mixture selected from nickel and cobaltmixed sulfide, coarse nickel sulfate, nickel oxide, nickel hydroxide,nickel carbonate, and nickel powder, with sulfuric acid or ammonia toobtain a nickel leaching solution (solution containing nickel),subjecting the nickel leaching solution to a purification step such assolvent extraction, ion exchange, and neutralization to obtain asolution from which impurity elements in the nickel leaching solutionhave been removed, and adding ammonia to the resulting solution to forma nickel ammine sulfate complex solution, in which nickel is containedin the form of nickel complex ions.

[Mixing Step]

In this step, a dispersant is first added to the nickel ammine sulfatecomplex solution prepared as described above, but an insoluble solid maybe added to the nickel sulfate amine complex solution without adding adispersant as described below.

A dispersant used here is not particularly limited as long as itcontains a sulfonate, but lignosulfonate is suitable as a material thatcan be inexpensively obtained industrially.

Further, the concentration of ammonium sulfate in the solution ispreferably in the range of 10 to 500 g/L. If the concentration exceeds500 g/L, the solubility will be exceeded, and crystals will beprecipitated. Further, since ammonium sulfate is newly produced byreaction, it is difficult to achieve a concentration of less than 10g/L.

<Addition of Insoluble Solid>

To the nickel ammine sulfate complex solution prepared as describedabove or the nickel ammine sulfate complex solution in which adispersant is added and adjusted, is added an insoluble solid which isinsoluble in the complex solution and used as a matrix forprecipitation.

The insoluble solid added here is not particularly limited as long as itis insoluble or has a low solubility in a nickel ammine sulfate complexsolution, an aqueous ammonium sulfate solution, or an alkali solution,and examples thereof that can be used include nickel powder, ironpowder, alumina powder, zirconia powder, and silica powder.

The present invention does not employ a conventional commonly-usedmethod of using seed crystals to precipitate a powder and obtaining aproduct including the seed crystals. In the present invention, after therequired precipitation (precipitation of nickel) on the surface of theinsoluble solid has been completed, the powder (precipitate of nickel)which has been precipitated and grown is separated from the insolublesolid, and only the powder portion is used as a product. According tosuch a method of the present invention, the influence on the productcaused by the properties as an impurity of the seed crystals themselveshas can be avoided.

The amount of the insoluble solid added is not particularly limited, butthe amount at which mixing by stirring can be achieved when theinsoluble solid is added to the nickel ammine sulfate complex solutionis selected depending on the type of the solid.

The shape and the size of the insoluble solid are not particularlylimited. However, since the nickel powder precipitated on the surfacemay be separated by mutually colliding or applying vibration as will bedescribed below, a suitable insoluble solid is that having a strengththat endures impact and friction and a shape with a smooth surface sothat nickel powder can be effectively separated.

Further, in terms of effective separation of nickel powder from theinsoluble solid, for example, an insoluble solid having a diameter ofabout 0.1 to 3 mm and a shape with no edges such as spherical orelliptical is easy to use in real operation.

Preferably, the insoluble solid is used as an insoluble solid of thepresent invention after debris and the like on the surface of theinsoluble solid is removed by giving collision and impact before nickelpowder is precipitated.

Further, an insoluble solid from which nickel powder has been separatedcan also be repeatedly used again after being subjected to pretreatmentsuch as washing as needed.

[Reduction and Precipitation Step]

Then, this step is a step of charging a reaction vessel resistant tohigh pressure and high temperature with the slurry formed by adding adispersant and an insoluble solid in the previous step and blowinghydrogen gas into the slurry stored in the reaction vessel to reducenickel complex ions in the slurry to precipitate nickel on the insolublesolid contained.

The temperature of the mixed slurry at this time, that is, reactiontemperature, is preferably in the range of 150 to 200° C. If thereaction temperature is less than 150° C., reduction efficiency will bereduced, and even if it exceeds 200° C., the reaction will not beaffected, but the loss of thermal energy will increase. Therefore, thesetemperatures are not suitable.

Further, the pressure of the gas phase part in the reaction vessel (thisrefers to a space part in the reaction vessel remaining after thesolution is stored in the reaction vessel) during the reaction ispreferably maintained at 1.0 to 4.0 MPa by feeding hydrogen gas. If thepressure is less than 1.0 MPa, reaction efficiency will be reduced, andeven if it is higher than 4.0 MPa, the reaction will not be affected,but the loss of hydrogen gas will increase. In this regard, the nickelcomplex ions in the slurry can also be reduced if hydrogen gas is blowninto the gas phase part in the reaction vessel instead of being blowninto the mixed slurry.

By reduction and precipitation treatment under such conditions, aprecipitate of nickel is formed on the insoluble solid and the nickelcontained in the solution can be extracted and recovered as aprecipitate of fine powdered nickel.

[Separation Step]

The nickel precipitate produced is in a state where it adheres to theinsoluble solid and cannot be utilized in this state. Therefore, in thisstep, the nickel precipitate formed on the surface of the insolublesolid is separated from the insoluble solid and recovered as nickelpowder.

Examples of specific separation methods of the nickel precipitateinclude a method of putting the whole insoluble solid and nickelprecipitate in water so that the nickel precipitate is not oxidized byheat generation, rotating the insoluble solid to collide the insolublesolids with each other to separate nickel powder on the surface, amethod of rotating the insoluble solid on a wet sieve to sift outseparated nickel powder at the same time, and a method of applying anultrasonic wave to a liquid to apply vibration to the insoluble solid toseparate nickel powder. A sieve having an opening that is finer than thesize of the insoluble solid can be used.

The nickel powder produced as described above can be used, for example,for nickel paste which is the internal constituent of multi-layerceramic capacitors, and, in addition, can be used for producing highpurity nickel metal by repeating the hydrogen reduction described aboveusing the recovered nickel powder as seed crystals to thereby growparticles.

EXAMPLES

The present invention will be described below using Examples andReference Examples.

Reference Example 1

[Mixing Step]

A solution containing a dispersant and a nickel ammine sulfate complexwas prepared by adding 191 ml of 25% aqueous ammonia and 20 g of sodiumlignosulfonate as the dispersant to a solution containing 75 g of nickel(nickel sulfate solution) and 330 g of ammonium sulfate and adjustingthe total volume of the solution to 1000 ml.

To this solution, was added 300 g of nickel powder having an averageparticle size (D50) of 125 μm as an insoluble solid used as a matrix forprecipitation followed by stirring to prepare a desired mixed slurry.

[Reduction and Precipitation Step]

Next, an inner cylinder of an autoclave was charged with the preparedmixed slurry; the mixed slurry was heated to 185° C. with stirring;hydrogen gas was blown into the mixed slurry while keeping thetemperature; and hydrogen gas was further fed so as to maintain thepressure in the inner cylinder of the autoclave at 3.5 MPa. After alapse of 140 minutes from the start of the feeding of hydrogen gas, thefeeding of hydrogen gas was stopped, and the inner cylinder was cooled.

[Separation Step]

After cooling, the mixed slurry in the inner cylinder was filtered toremove the insoluble solid having nickel precipitate formed on thesurface; the insoluble solid was then put in a wet sieve having anopening of 100 μm; and vibration was applied to the insoluble solid toseparate the precipitated nickel powder from the insoluble solid as amatrix.

When the recovered nickel powder was observed, it was verified that finenickel powder was produced as shown in FIG. 2.

Reference Example 2

[Mixing Step]

A solution containing a dispersant and a nickel ammine sulfate complexwas prepared by adding 191 ml of 25% aqueous ammonia and 10 g of sodiumlignosulfonate as a dispersant to a solution containing 75 g of nickel(nickel sulfate solution) and 330 g of ammonium sulfate and adjustingthe total volume of the solution to 1000 ml. To this solution, was added75 g of zirconia balls each having a diameter of 1 mm as an insolublesolid used as a matrix for precipitation to prepare a mixed slurry.

[Reduction and Precipitation Step]

Next, an inner cylinder of an autoclave was charged with the mixedslurry; the mixed slurry was then heated to 185° C. with stirring;hydrogen gas was blown into the mixed slurry while keeping thetemperature; and hydrogen gas was fed so as to maintain the pressure inthe inner cylinder of the autoclave at 3.5 MPa. After a lapse of 65minutes from the start of the feeding of hydrogen gas, the feeding ofhydrogen gas was stopped, and the inner cylinder was cooled.

[Separation Step]

After cooling, the mixed slurry in the inner cylinder was filtered toremove the insoluble solid having nickel precipitate formed on thesurface; the removed insoluble solid was then put in a wet sieve havingan opening of 500 μm; and vibration was applied to the insoluble solidto separate the precipitated nickel powder from the insoluble solid as amatrix.

When the recovered nickel powder was observed, it was verified that finenickel powder was produced as shown in FIG. 3.

Comparative Example 1

[Separation Step]

A solution containing a dispersant and a nickel ammine sulfate complexwas prepared by adding 191 ml of 25% aqueous ammonia and 5 g of sodiumlignosulfonate as a dispersant to a solution containing 75 g of nickel(nickel sulfate solution) and 330 g of ammonium sulfate and adjustingthe total volume of the solution to 1000 ml. The next operation wasperformed without adding an insoluble solid used as a matrix forprecipitation to this solution.

[Reduction and Precipitation Step]

An inner cylinder of an autoclave was charged with the preparedsolution; the solution was then heated to 185° C. with stirring;hydrogen gas was blown into the solution while keeping the temperature;and hydrogen gas was fed so as to maintain the pressure in the innercylinder of the autoclave at 3.5 MPa. After a lapse of 60 minutes fromthe start of the feeding of hydrogen gas, the feeding of hydrogen gaswas stopped, and the inner cylinder was cooled.

[Separation Step]

After cooling, the solution in the inner cylinder was filtered, butnickel powder could not be recovered, and plate-shaped scaling of nickeloccurred on the side wall of the inner cylinder and on the stirrer.

Example 1

[Mixing Step]

A solution containing a nickel ammine sulfate complex was prepared byadding 13 ml of 25% aqueous ammonia to a solution containing 75 g ofnickel (nickel sulfate solution) and 330 g of ammonium sulfate andadjusting the total volume of the solution to 1000 ml. To this solution,was added 5 g of electrolytic iron powder as a matrix for precipitationto prepare a mixed slurry.

[Reduction and Precipitation Step]

Next, an inner cylinder of an autoclave was charged with the mixedslurry; the mixed slurry was then heated to 185° C. with stirring; andhydrogen gas was blown into the mixed slurry for 10 minutes at a flowrate of 0.2 L/min while keeping the temperature. The pressure in theinner cylinder of the autoclave during the reaction showed 1.0 MPa.Subsequently, the feeding of hydrogen gas was stopped, and the innercylinder was cooled.

[Separation Step]

After cooling, the slurry in the inner cylinder was filtered to removethe insoluble solid having nickel precipitate formed on the surfacethereof, and nickel powder was recovered in the same manner as inReference Example 1.

When the recovered powder was observed, it was verified that fine nickelpowder was produced as shown in FIG. 4. Note that when FIG. 4 iscompared with FIG. 2 in the case where a dispersant was added, the shapeof nickel powder looks slightly non-uniform and rough, but there ispractically no problem.

Reference Example 4

[Mixing Step]

A solution containing a nickel ammine sulfate complex was prepared byadding 191 ml of 25% aqueous ammonia and 5 g of sodium lignosulfonate asa dispersant to a solution containing 75 g of nickel (nickel sulfatesolution) and 330 g of ammonium sulfate and adjusting the total volumeof the solution to 1000 ml. To this solution, was added 75 g of aluminapowder having a size of 200 meshes as an insoluble solid used as amatrix for precipitation to prepare a mixed slurry.

[Reduction and Precipitation Step]

Next, an inner cylinder of an autoclave was charged with the mixedslurry; the mixed slurry was then heated to 185° C. with stirring;hydrogen gas was blown into the mixed slurry while keeping thetemperature; and hydrogen gas was fed so as to maintain the pressure inthe inner cylinder of the autoclave at 3.5 MPa. After a lapse of 90minutes from the start of the feeding of hydrogen gas, the feeding ofhydrogen gas was stopped, and the inner cylinder was cooled.

[Separation Step]

After cooling, the slurry in the inner cylinder was filtered to removethe insoluble solid having nickel precipitate formed on the surfacethereof, and nickel powder was recovered in the same manner as inReference Example 1.

When the recovered powder was observed, it was verified that fine nickelpowder was produced on alumina as a matrix as shown in FIG. 5. (Theplaces where nickel powder was produced were shown by enclosing themwith circles.)

Reference Example 5

[Mixing Step]

A solution containing a nickel ammine sulfate complex was prepared byadding 191 ml of 25% aqueous ammonia and 5 g of sodium lignosulfonate asa dispersant to a solution containing 75 g of nickel (nickel sulfatesolution) and 330 g of ammonium sulfate and adjusting the total volumeof the solution to 1000 ml. To this solution, was added 75 g of silicapowder having a D50 of 38 μm as an insoluble solid used as a matrix forprecipitation to prepare a mixed slurry.

[Reduction and Precipitation Step]

Next, an inner cylinder of an autoclave was charged with the mixedslurry; the mixed slurry was then heated to 185° C. with stirring;hydrogen gas was blown into the mixed slurry while keeping thetemperature; and hydrogen gas was fed so as to maintain the pressure inthe inner cylinder of the autoclave at 3.5 MPa. After a lapse of 90minutes from the start of the feeding of hydrogen gas, the feeding ofhydrogen gas was stopped, and the inner cylinder was cooled.

[Separation Step]

After cooling, the slurry in the inner cylinder was filtered to removethe insoluble solid having nickel precipitate formed on the surface, andnickel powder was recovered in the same manner as in Reference Example1.

When the recovered powder was observed, it was verified that fine nickelpowder was produced as shown in FIG. 6.

The invention claimed is:
 1. A method for producing nickel powder,sequentially comprising: a mixing step of adding, to a solutioncontaining a nickel ammine sulfate complex, an insoluble solid that isinsoluble in the solution to form a mixed slurry, the insoluble solidhaving a shape with a smooth surface, and the mixing step being carriedout without adding a dispersant; a reduction and precipitation step ofcharging a reaction vessel with the mixed slurry and then blowinghydrogen gas into the mixed slurry while maintaining a pressure of a gasphase part in the reaction vessel at 1.0 to 4.0 MPa, to reduce nickelcomplex ions contained in the mixed slurry to form nickel precipitate ona surface of the insoluble solid; and a separation step of separatingthe nickel precipitate on the surface of the insoluble solid from thesurface of the insoluble solid to form nickel powder.
 2. The method forproducing nickel powder according to claim 1, wherein ammonium sulfateincluded in the solution containing a nickel ammine sulfate complex hasa concentration of 10 to 500 g/L.
 3. The method for producing nickelpowder according to claim 2, wherein, in the reduction step, the mixedslurry when the hydrogen gas is blown has a temperature of 150 to 200°C.
 4. The method for producing nickel powder according to claim 3,wherein the insoluble solid is one or a combination selected from amongnickel, alumina, zirconia, iron, and silica.
 5. The method for producingnickel powder according to claim 1, wherein, in the reduction step, themixed slurry when the hydrogen gas is blown has a temperature of 150 to200° C.
 6. The method for producing nickel powder according to claim 5,wherein the insoluble solid is one or a combination selected from amongnickel, alumina, zirconia, iron, and silica.
 7. The method for producingnickel powder according to claim 1, wherein the insoluble solid is oneor a combination selected from among nickel, alumina, zirconia, iron,and silica.